Folate deficient tumor microenvironment promotes epithelial-to-mesenchymal transition and cancer stem-like phenotypes.

Yen-Hao Su,Yan-Jiun Huang,Chien-Min Lin,Alexander Th Wu,Yu-Kai Sue,Tse-Hung Huang,Tsan-Zon Liu,Thanh-Tuan Huynh,Wen-Chien Huang,Michael Hsiao

doi:10.18632/oncotarget.8910

Abstract

Clinically, serum level of folate has been negatively correlated to the stage and progression of liver cancer. Nevertheless, the functional consequence of folate deficiency (FD) in malignancy has not been fully investigated. Human hepatocellular carcinoma (HCC) cells (as study model) and other cancer types such as lung and glioma were cultured under folate deficient (FD) and folate complete (FD) conditions. Molecular characterization including intracellular ROS/RNS (reactive oxygen/nitrogen species), viability, colony formation, cancer stem-like cell (CSC) phenotype analyses were performed. In vivo tumorigenesis under FD and FC conditions were also examined. FD induced a significant increase in ROS and RNS, suppressing proliferative ability but inducing metastatic potential. Mesenchymal markers such as Snail, ZEB2, and Vimentin were significantly up-regulated while E-cadherin down-regulated. Importantly, CSC markers such as Oct4, β-catenin, CD133 were induced while PRRX1 decreased under FD condition. Furthermore, FD-conditioned HCC cells showed a decreased miR-22 level, leading to the increased expression of its target genes including HDAC4, ZEB2 and Oct4. Finally, xenograft mouse model demonstrated that FD diet promoted tumorigenesis and metastasis as compared to their FC counterparts. Our data provides rationales for the consideration of folate supplement as a metastasis preventive measure.

Highlights

Liver cancer ranks the fifth most common cancer globally and the high incidence of distant metastasis makes it the third most common cause of cancer mortality [1]
Because liver is the major site for folate storage and susceptible to folate deficiency (FD), deprivation in this micronutrient may contribute to chromosomal breaks and deleterious alterations in gene expression leading to genetic instability and carcinogenesis [9,10,11]
We first demonstrated that folate deprivation elicited a significant increase in both reactive oxygen and nitrogen species in both SK-Hep1 and Mahlavu cells; FD culture led to the suppressed proliferation and colony formation

Summary

Introduction

Liver cancer ranks the fifth most common cancer globally and the high incidence of distant metastasis makes it the third most common cause of cancer mortality [1]. A previous clinical study has established an inverse correlation between the serum folate level and tumor size, multiplicity and metastasis; when disease progression was categorized into stages I to IV, serum folate decreased as disease stage progressed [17]. Another larger cohort study demonstrated that higher folate level in red blood cells was associated with reduced risk of hepatocarcinogenesis [18]. It has been suggested that folate may play important roles in preventing tumorigenesis in different cancer types [19,20,21] These findings have implicated the importance of folate status in the carcinogenesis of hepatocellular carcinoma and others. Mechanistic explanations linking FD to the promotion of distant metastasis of liver cancer cells remains to be elucidated

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Discussion

Conclusion